Soil decontamination apparatus and methods of decontaminating soil

Abstract

A soil decontamination apparatus is based on a heating operation performed on soil to be contaminated to vaporize and burn off hydrocarbons. The soil is fed into a drum drier at a constant rate which is related to the moisture contents in the soil and the energy available from the burner of the drum drier. Soil particles in the form of dust which become entrained in the hot gases which are used in the decontamination process are removed from the gas stream and are recombined with the base material of the soil in a region of the drum drier which is substantially devoid of gas flow. The substantially calm atmosphere in the region of the drum drier in which the recombination takes place permits the fines to be mixed with the base material without the fines again being carried off by gaseous movement. A soil reconditioning is provided for in an isolated third zone of the drum drier.

What is claimed is: 
     
       1. Apparatus for decontaminating soil comprising: a drum drier including a heating and drying zone and a material combination zone;   means for heating soil, the soil including a base material and soil particles capable of becoming entrained in a gaseous flow, in a hot decontaminating gas stream to a temperature above the vaporization temperature of contaminants within the soil, the soil heating means comprising means for generating and passing a stream of hot gases through the heating and drying zone;   means for feeding soil at a predetermined rate into the heating and drying zone;   means for advancing the soil through the drum drier from heating and drying zone into the material combination zone out of exposure to said gas stream;   means for removing soil particles carried by said gas stream from said gas stream; and   means for combining such soil particles after removal from said gas stream within the material combination zone with the base material subsequent to the base material having been advanced to the material combination zone out of exposure to said gas stream and with substantially no gaseous movement.   
     
     
       2. Apparatus for decontaminating soil according to claim 1, wherein the soil feeding means comprises: means for separating soil into at least two gradations according to particle size;   a crusher for comminuting soil;   means for feeding a first gradation of soil through said crusher thereby comminuting the soil;   a main feed conveyor means for feeding soil to the heating means, the main feed conveyor means including a main feed conveyor and means for determining the feed rate of material being fed to the heating means by the main feed conveyor;   means for loading the soil comminuted by the operation of said crusher onto the main feed conveyor;   means for temporarily storing a second gradation of the at least two gradations of soil;   means for determining the feed rate of soil to the heating means as a result of the operation of the loading means loading comminuted soil onto the main feed conveyor; and   means for selectively loading soil from the temporary storing means onto the main feed conveyor to supplement soil loaded by the operation of the loading means for loading comminuted soil onto the main feed conveyor to feed soil at a predetermined rate to the heating means.   
     
     
       3. Apparatus for decontaminating soil according to claim 1, the drum drier further comprising at least one zone for reconstituting the soil, the soil reconstituting zone being disposed adjacent the material combination zone, isolated from gaseous flow for decontaminating soil, means disposed between the material combination zone and the soil reconstituting zone for restricting gaseous flow in a direction opposite to the direction of advance of material through the drum in response to the operation of the advancing means, and means communicating with said at least one soil reconstitution zone for reconstituting soil with water. 
     
     
       4. Apparatus for decontaminating soil according to claim 3, wherein said means for heating soil comprises a burner head disposed at one end of said heating and drying zone and means for generating hot gases at the burner head and for directing the hot gases to flow through the heating and drying zone against the general flow of soil through the drum drier, said means for advancing soil through the drum drier out of the exposure to said gas stream comprising flighting for advancing material from the heating and drying zone past the burner head through the material combination zone and into and through such soil reconstituting zone. 
     
     
       5. A method of decontaminating soil comprising: feeding soil to be decontaminated at a constant rate into a heating and drying zone of a drum drier;   advancing the soil through the heating and drying zone of the drum drier;   generating a stream of hot gases and flowing the stream of hot gases through the heating and drying zone at a rate to heat the soil advancing through the heating and drying zone above a vaporization temperature of contaminants within the soil, the stream of hot gases entraining at least a portion of the soil;   exhausting the stream of hot gases including the entrained portion of the soil from the drum drier;   advancing the portion of the soil remaining within the heating and drying zone of the drum drier from the heating and drying zone to a zone with substantially no gaseous movement;   separating the entrained soil from the hot gases; and   recombining the soil separated from the hot gases with the remaining soil within the zone with substantially no gaseous movement.   
     
     
       6. A method according to claim 5, further comprising reconstituting the recombined soil with water in a further zone substantially isolated from the heating and drying zone and the zone with substantially no gaseous movement. 
     
     
       7. A method according to claim 6, further comprising: removing gases including steam generated during the step of reconstituting the recombined soil, mixing the removed gases and steam with gases from the stream of hot gases and passing the mixed gases including the removed gases through a filter. 
     
     
       8. A method according to claim 6, further comprising, after separating the entrained soil from the hot gases, advancing the hot gases into communication with an afterburner for substantially burning residual hydrocarbons in the hot gases, removing gases including steam generated during the step of reconstituting the recombined soil, and combining the removed gases and steam with exhaust gases from the afterburner thereby cooling the exhaust gases. 
     
     
       9. A method according to claim 8, further comprising routing the combined removed gases, steam and exhaust gases from the afterburner through a final filter before releasing such combined gases into the atmosphere. 
     
     
       10. Apparatus for decontaminating soil comprising: a drum drier including an axially rotatable drum having a material feed end and a material discharge end opposite the material feed end, a decontamination zone within the drum adjacent the feed end of the drum, a combination zone adjacent the decontamination zone, means for advancing materials longitudinally from the material feed end through the decontamination zone and through the combination zone toward the material discharge end of the drum, and a burner disposed axially with respect to said drum for generating a hot gas stream within the decontamination zone of the rotatable drum to flow through the decontamination zone toward the feed end of the drum in a counterflow direction to the material advance through the drum;   means for removing the stream of hot gases at the feed end of the drum;   means for feeding soil at a predetermined rate into the material feed end of the drum and into engagement with the material advancing means of the drum, for the soil to advance in the direction of the discharge end against the flow of hot gases in the decontamination zone of the drum;   means for filtering the hot gases removed at the feed end of the drum prior to releasing them to the atmosphere to thereby separate soil entrained within the hot gas stream from such stream prior to releasing the gases into the atmosphere; and   means for combining the soil separated from the hot gas stream by the filtering means with the soil advancing through the drum within the combination zone of the drum immediately past the flame region of the burner.   
     
     
       11. Apparatus for decontaminating soil according to claim 10, wherein the means for filtering the hot gases removed at the feed end comprises first and second filter means coupled in series into the path of hot gases, and wherein an afterburner is disposed within the path of the hot gases, the afterburner burning hydrocarbon gases of the hot gas stream to carbon dioxide and water vapor, the apparatus further comprising means for cooling the hot gases after the gases pass through the afterburner and before the gases are filtered by the second filter means. 
     
     
       12. Apparatus for decontaminating soil according to claim 11, further comprising means, including a supply of water, for reconstituting the soil with water. 
     
     
       13. Apparatus for decontaminating soil according to claim 12, wherein the means for cooling the gases comprises fluid ducts coupled to the soil reconstituting means for combining the hot gases with steam generated by the operation of the soil reconstituting means. 
     
     
       14. Apparatus for decontaminating soil according to claim 10, wherein the soil feeding means comprises: means for separating soil into at least two gradations according to particle size;   a crusher for comminuting a first gradation of soil;   means for feeding a first gradation of soil through said crusher thereby comminuting the soil;   a main feed conveyor means for feeding soil into the feed end of the drum, the main feed conveyor means including a main feed conveyor and means for determining the rate at which the soil is fed into the feed end of the drum;   means for loading the soil comminuted by the operation of the crusher onto the main feed conveyor;   means for temporarily storing a second gradation of the at least two gradations of soil;   means for determining the feed rate of soil into the feed end of the drum as a result of the operation of the loading means loading comminuted soil onto the main feed conveyor; and   means for selectively adding soil from the temporary storing means to the main feed conveyor when the feed rate as a result of the operation of the loading means is less than the predetermined feed rate of soil into the feed end of the drum.   
     
     
       15. Apparatus for decontaminating soil according to claim 10, wherein the means for filtering comprises a filter house mounted across the drum drier to straddle the drum drier, the filter house comprising a header section coupled to the feed end of the drum of the drum drier to receive the hot gases from the drum drier, and means for advancing the separated soil toward and into the combination zone of the drum.